The efficiency of natural zeolite to remove ammonium from artificial wastewater (ammonium aqueous solutions) and to treat second cheese whey was examined, aiming to recover nitrogen nutrients that can be used for further applications, such as slow-release fertilizers. Sorption experiments were performed using artificial wastewater and zeolite of different granulometries (i.e., 0.71–1.0, 1.8–2.0, 2.0–2.8, 2.8–4.0, and 4.0–5.0 mm). The granulometry of the zeolite had no significant effect on its ability to absorb ammonium. Nevertheless, smaller particles (0.71–1.0 mm) exhibited quicker NH₄⁺-N adsorption rates of up to 93.0% in the first 10 min. Maximum ammonium removal efficiency by the zeolite was achieved at ammonium concentrations ranging from 10 to 80 mg/L. Kinetic experiments revealed that chemisorption is the mechanism behind the adsorption process of ammonium on zeolite, while the Freundlich isotherm model fitted the experimental data well. Column sorption experiments under batch operating mode were performed using artificial wastewater and second cheese whey. Column experiments with artificial wastewater showed high NH₄⁺-N removal rates (over 96% in the first 120 min) for all granulometries and initial NH₄⁺-N concentrations tested (200 and 5000 mg/L). Column experiments with second cheese whey revealed that natural zeolite can remove significant organic loads (up to 40%, 14.53 mg COD/g of zeolite) and NH₄⁺-N (about 99%). For PO₄³⁻-P, the zeolite appeared to saturate after day 1 of the experiments at a removal capacity of 0.15 mg P/g of zeolite. Desorption experiments with water resulted in low NH₄⁺-N and PO₄³⁻-P desorption rates indicating that the zeolite could be used as a substrate for slow nitrogen release in soils.

The biodegradation of municipal solid waste (MSW) was investigated in simulated bioreactor landfills under aerobic conditions. The bioreactors were operated to determine Two constructed wetland systems, treating domestic wastewater, are compared in terms of performance and costs. One is a free water surface (FWS) wetland system located in Pompia, Crete, south Greece, and the other one is a vertical subsurface flow (VSF) wetland system located in Gomati, Chalkidiki, north Greece. The FWS system is designed for 1200 p.e. Its construction cost was [euro]305,000, and the capital, operation and maintenance cost was [euro]22.07 p.e.⁻¹ yr⁻¹ or [euro]0.50 m⁻³ of influent. The VSF system is designed for 1000 p.e. Its construction cost was [euro]410,850, and the capital, operation and maintenance cost was [euro]36.81 p.e.⁻¹ yr⁻¹ or [euro]0.56 m⁻³ of influent. Both systems achieved high removal rates for BOD₅, COD, TSS, TKN, phosphorus, TC, and FC, which makes them ideal for small communities in the Mediterranean region.